THostResolver how-to?
lazarus / 38-Networking and Web Programming

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dg4fac · 2018-02-04 15:42

I tried for several hours now to bring THostResolver to translate an
IP to a computer name. I have four edit fields and the following code
on edit field 1 (where I type an IP in text form and hit the Enter
key):

procedure TForm1.Edit1KeyUp(Sender: TObject; var Key: Word; Shift:
TShiftState);
var
  host:THostResolver;
begin
If Key=13 Then
  begin
  host := THostResolver.Create(nil);
  if host.NameLookup(Edit1.Text) then
    begin
    Edit2.Text := ...;
    Edit3.Text:=IntToStr(host.AddressCount);
    Edit4.Text:=IntToStr(host.AliasCount);
    end else
    Edit2.Text := '';
  host.Free;
  end;
end;

Edit3 and Edit4 work fine, but whatever I try to write to Edit2 is not
the desired computer name. host.ResolvedName should be the name, but
it simply repeats the IP string that I entered.

By going through the resolve.pp I did not find any hint. It remains
unclear what the author means by the terms he uses (not very clearly
documented).

Does someone has some hint?

gerd

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TRon · 2018-02-04 17:00

Quote from: dg4fac on February 04, 2018, 04:42:29 pmI tried for
several hours now to bring THostResolver to translate an IP to a
computer name.

Code: [Select]Function GetHostNameByAddress(const AnAddress: String):
String;
var
  Resolver: THostResolver;
begin
  Result := '';
  if AnAddress = '' then exit;
  Resolver := THostResolver.Create(nil);
  try
    if Resolver.AddressLookup(AnAddress) then
      Result := Resolver.ResolvedName
  finally
    FreeAndNil(Resolver);
  end;
end;
Note that the order of the ip address matters on certain platforms:
Code: [Select]HostName := GetHostNameByAddress('1.0.0.127');

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dg4fac · 2018-02-04 17:50

Quote from: TRon on February 04, 2018, 06:00:45 pmQuote from: dg4fac
on February 04, 2018, 04:42:29 pmI tried for several hours now to
bring THostResolver to translate an IP to a computer name.

QuoteCode: [Select]Function GetHostNameByAddress(const AnAddress:
String): String;
var
  Resolver: THostResolver;
begin
[...]
    if Resolver.AddressLookup(AnAddress) then
      Result := Resolver.ResolvedName
[...]

That is one of the things that confuse me in resolve.pp: the use of
the terms "Address" and "Name". In my view the "Name" is
"www.dg4fac.de", the "Address" is 217.160.231.116. As I am searching
for the name I thought that "NameLookup" should be the correct
function. As "AddressLookup" with 217.160.231.116 fails I thought that
I am correct using "NameLookup".

QuoteNote that the order of the ip address matters on certain
platforms:
Code: [Select]HostName := GetHostNameByAddress('1.0.0.127');
Confusing, like naming me drahreG. The least significant first, sounds
nerdy. I tried that with 116.231.160.217, and it is even more
confusing: it returns "kundenserver.de", where the site is hosted. And
even more confusing: nslookup in Windows with 217. ... delivers
"www.dg4fac.de".

I am about to give up.

gerd

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TRon · 2018-02-05 05:33

Quote from: dg4fac on February 04, 2018, 06:50:42 pmThat is one of the
things that confuse me in resolve.pp: the use of the terms "Address"
and "Name". In my view the "Name" is "www.dg4fac.de", the "Address" is
217.160.231.116. As I am searching for the name I thought that
"NameLookup" should be the correct function. As "AddressLookup" with
217.160.231.116 fails I thought that I am correct using "NameLookup".
It is confusing, especially since documentation for these components
are pretty much non existent

QuoteConfusing, like naming me drahreG. The least significant first,
sounds nerdy.
Nothing nerdy about that. See also network byte ordering.

Usually (and simply put) there is a start-point (host), end-point
(remote) and in between (internet). host and remote does not have to
know anything about each other and can be totally different
systems/platforms. The only agreement is the network byte ordering and
some internet related rfc's.

QuoteI tried that with 116.231.160.217, and it is even more confusing:
it returns "kundenserver.de", where the site is hosted. And even more
confusing: nslookup in Windows with 217. ... delivers "www.dg4fac.de".
kundenserver.de looks correct to me ? As can also be verified with
online tools like ipchecker